For instance, for an internal combustion engine of a vehicle, in order to prevent release of fuel vapor evaporated from a fuel tank of the vehicle into the outside, a canister that is capable of adsorbing and desorbing the fuel vapor is provided. The canister temporarily adsorbs the fuel vapor that is generated after a vehicle stop etc., and desorbs an adsorbed fuel component together with a fresh atmospheric air during a drive then burns the fuel component in the internal combustion engine.
Here, as an adsorbent of the canister, although activated carbon having minute pore that catches the fuel component is widely used, Patent Document 1 has proposed a technique of, as a so-called molded activated carbon adsorbent obtained by molding activated carbon powder into a granular shape or a particle through a binder, forming macroscopic pore that is greater in size than microscopic pore of the activated carbon itself, by adding meltable core that sublimates or decomposes at a baking to the activated carbon powder together with the binder then molding and baking this mixture. A size of the microscopic pore of the activated carbon itself is less than 100 nm, while a size of the macroscopic pore formed by the meltable core is 100 nm or greater. The macroscopic pore functions as a sort of path through which a molecule(s) of the evaporated fuel can pass. By forming the macroscopic pore that serves as the path at an inside of the adsorbent in this manner, it is possible to increase a size of the adsorbent while ensuring an adsorbing/desorbing performance.
In view of a flow resistance which is important as the canister, it is desirable that the granular adsorbent should have a measure of size, e.g. a particle diameter of about 4 mm that is disclosed in the Patent Document 1. However, in the case of such large-sized adsorbent, a part of activated carbon component, which exists at the inside of each adsorbent, does not contribute to the adsorption/desorption of the evaporated fuel, and thus the adsorbing/desorbing performance of the large-sized adsorbent becomes low as compared with minute adsorbent. Therefore, in the case of adsorbent having the large-sized particle diameter disclosed in the Patent Document 1, in order to ensure the adsorbing/desorbing performance, a proportion of the macroscopic pore to the microscopic pore is quite high. As a consequence, this case has such defects that strength of the adsorbent is low.
That is to say, the canister using the related art adsorbent can not satisfy the adsorbing/desorbing performance of the fuel vapor, the flow resistance as the canister and the strength of the adsorbent at the same time.